Charge design for carbon fibre sheet moulding compounds—Impact on morphology and mechanical performance

Abstract

Compression moulded carbon fibre reinforced sheet moulding compounds aim to maximize the mechanical performance of discontinuous fibre composites, while maintaining low cycle times. The shape of the charge governs their in-mould flow behaviour, which is one of the most important factors influencing their mechanical performance. While high amounts of flow and the presence of weld lines have been identified as the major performance detractors, the practical implications of these finding on how charges should be designed have not yet been investigated in detail. The present study considers different charge configurations based on challenges that arise when balancing repeatable high performance and manufacturing efficiency in an industrial context. The influence of these configurations on the local internal microstructure is measured with micro-computed tomography and closely associated with the corresponding local mechanical performance measured using digital image correlation. While a charge closely resembling the part indeed yields the most reliable quasi-isotropic results, some in-mould flow aids in evacuating trapped gases and is in many scenarios preferable to piecing together charges from sheet moulding compound patches, thus introducing weld lines. Notably, an even charge coverage is important, to avoid local complex flow patterns, which highly distort the material and constitute significant weak spots.